Liquid-liquid extraction can be used for the recovery of solutes in an aqueous system. Liquid-liquid extraction generally employs the principle of contacting a solute-bearing aqueous liquid, with an organic liquid having an affinity for the solutes. The liquid and organic phase are first mixed to promote transfer of solute from the aqueous to the organic phase, and then allowed to coalesce and settle by gravity whereupon at least a portion of the solute is now dispersed in the organic extractant phase.
Mixer-settlers can be used for liquid-liquid extraction. Mixer-settlers typically include a mixing chamber and a settling chamber. The organic extractant liquid and the aqueous liquid are normally mixed in the mixing chamber and then overflow into the settling chamber, where the phases are allowed to separate. The end of the settling chamber can include two weirs to separate out the liquid phases. Specifically, the lighter organic phase overflows into a first weir having an opening at the top of the tank, and the heavier aqueous phase flows into a second weir having an opening at the bottom of the tank. A schematic of such a conventional overflow-mixer settler is provided in FIG. 1.
A drawback associated with the conventional mixer-settler design described above is that of cross-contamination of the phases. That is, organic fluid entrained in the aqueous fluid can flow into the aqueous weir. Another drawback associated with such current mixer-settler designs is air entrainment, which is a source of “crud.” Air entrainment occurs because standard organic weirs are overflow, that is the top of the organic phase overflows into the top of the organic weir.
Accordingly, it is desirable to provide a mixer-settler apparatus that alleviates cross-contamination of phases and/or air entrainment. It is also desirable to provide a method for liquid-liquid extraction in mixer-settlers that alleviates cross-contamination of phases and/or air entrainment.